1. Field of the Invention
This invention relates to a continuously variable speed ratio transmission. More particularly, the invention pertains to such a transmission wherein a differential speed ratio traction drive unit produces the continuously variable speed ratios in combination with a hydraulic torque converter located behind the traction unit in a driveline that includes a torque splitting gearset.
2. Description of the Prior Art
A continuously variable transmission can produce a wide range of speed and torque ratios through an infinite number of steps. It is known in the prior art that the range of ratios can be varied by a traction drive unit which produces the ratio variations depending upon the radius at which a friction drive element contacts the driving and driven disks of the traction unit. U.S. Pat. Nos. 2,181,380 and 2,446,462 disclose power transmissions employing traction drive units. Traction drive units of this type transmit torque from the driving element to the driven element by developing friction forces on the surface of an intermediate element at the points of contact with the driving and driven members.
Traction drives are subject to excessive wear on the drive surfaces because power is transmitted by friction, yet frequent service and replacement of the drive elements is unacceptable in an automotive transmission. Furthermore, power losses particularly those resulting from slippage at the mating friction surfaces are a recognized problem that can produce unaccepatable pulsing when the surfaces lose and regain driving engagement.